This invention extends the teachings of my U.S. Pat. No. 4,114,688, which is incorporated herein by reference.
It is well known in the art how to generate useful fuels from coal in situ. It may be briefly stated that an underground coal seam is consumed in situ by setting the coal afire, injecting reactants into one well while withdrawing the products of reaction from a nearby second well, both wells being drilled from the surface of the earth into the coal seam. Reactants commonly include air, oxygen, steam, carbon dioxide and the like. Products of underground reactions include such fuels as hydrogen, carbon monoxide, methane and other hydrocarbons; condensible coal liquids; and non-combustibles such as carbon dioxide, water vapor, nitrogen and fly ash.
In commercial practice a multiplicity of injection wells and withdrawal wells are operated in pairs to provide the desired volume of useful products on a sustained basis. From the withdrawal or production wells it is relatively easy to separate the condensible coal liquids from the gas stream and thus recover a liquid product rich in coal chemicals. Likewise, fly ash or particulate matter may be separated from the produced gas stream. Separating hydrogen, carbon monoxide, carbon dioxide and methane into individual gas streams of high purity is somewhat more complicated, but there are many commercial methods available for making such separation.
In gasifying coal in situ, the underground reactors located in the coal seam between each pair of wells have capacities for producing enormous quantities of useful gases. Of particular interest in this invention are the generated gases comprised of hydrogen, carbon monoxide and carbon dioxide. Of lesser interest are methane and condensible coal liquids, although these products may be reformed in surface facilities to provide useful fuels such as methanol, hydrogen, carbon monoxide and ammonia--all of which are suitable fuels for fuel cell operation.
In common commercial practice of generating electricity from fuels, the selected fuel is burned for its heat content, resultant heat is applied to water, water is converted into steam, steam is expanded through a turbine, the turbine spins a generator, which, in turn, produces electricity. In this relatively simple sequence of events an enormous quantity of water is consumed and thus removed from local water supplies. For each pound of steam expanded through the turbine, a corresponding pound of water must be evaporated into the atmosphere, such evaporation generally occuring from the adjacent cooling lake or from the cooling tower. This large scale evaporation of water is of little consequence in the portions of the United States receiving abundant rainfall; however, it is a very serious problem in the arid western states. The arid western states contain large reserves of useful fuels, particularly coal, which are expected to be vital to the welfare of the United States in the years ahead. Thus a series of serious problems arise in the effective utilization of coal reserves. For example, in the use of coal for generation of electricity, mine-mouth generating stations take a serious bite out of local water supplies while requiring long distance transmission lines to market. Generating stations located near markets require long distance transport of coal, which, unfortunately must be shipped with a substantial amount of its weight and volume being unburnable impurities. An obvious improvement could be made by generating electricity at the mine-mouth, or nearby, using procedures that do not require withdrawals from the local water supply. Still further improvements can be made by eliminating the requirement of mining the coal in the first place, then generating electricity with a process that also generates, rather than consumes, water. It is one object of the present invention to teach such methods.
It is well known in the art how to generate electricity in fuel cells, such fuel cells having been in existance for more than 100 years. In the earlier years fuel cells were of little practical importance because of their requirement for relatively expensive fuels, such as hydrogen, that could not compete with abundant natural gas, fuel oil and coal. In recent times, particularly in the past 20 years, significant improvements have been made in the construction and reliable operation of fuel cells in support of the NASA space program. In the common commercial practice of converting heat by the burning of fuel, maximum efficiency in the generation of electricity is in the order of 40%. On the other hand, maximum efficiencies of electricity from fuel cells approach 100%. The fuel cell process can essentially eliminate the requirement to convert the fuel's chemical energy into heat, thus substantially all of the chemical energy can be converted directly into electricity. In these types of fuel cells, electrical loads can be generated almost instantaneously with no requirement for warm up for start up, thus providing flexibility in balancing generated electricity to match the varying power demands during a 24 hour day. Some types of fuel cells, however, in the interest in broadening the types of useful fuels, do require some outside heat with a resultant loss of efficiency. Fuel cells operating at elevated temperatures routinely attain higher efficiencies than steam-electric generating systems.
With the dramatic escalation of prices for petroleum products in recent years, coupled with the probability of such increasing prices continuing indefinitely, the price advantage of such fuels is rapidly eroding as compared to the cost of fuels suitable for fuel cells. It thus follows that fuel cells are a likely condidate for future electric power generation.
Fuel cells are relatively simple devices normally assembled sandwich fashion, the center being an electrolyte. Typically on one side of the electrolyte is an anode and on the other a cathode. A gas chamber is attached to the anode to receive the fuel and a second gas chamber is attached to the cathode to receive the oxidizer. The electrolyte is selected to permit free passage of ions, while barring the passage of gas molecules, gas atoms and electrons. With the aid of catalysts the fuel is chemisorbed onto the anode and the oxidizer is chemisorbed onto the cathode. Thus the stage is set for negative ions to accumulate on the anode while positive ions collect on the cathode, completing the electro-chemical reactions of converting fuel into electricity.
One type of fuel cell of particular interest to the present invention is the cell that uses hydrogen as the fuel. This type of cell received a great deal of development in support of the Apollo moon shots conducted by NASA. In addition to generating electricity, quietly and at low temperature, the cells also generated by-product water useful both as drinking water and as cooling water.
The ability to generate water while generating electricity is of more than passing interest in the arid western portion of the United States, the location of most of the coal reserves suitable for in situ production. Thus the use of hydrogen fuel cells can overcome one serious objection to sitting electric power generating stations in the west. It is unlikely, however, that hydrogen fuel cells alone will suffice in view of the other fuels also available from coal. A combination of cells, some using hydrogen and some using carbon monoxide, would provide a more desirable balance.
One cell of interest is the so-called hot carbonate cell. In this particular design the electrolyte is molten carbonate (CO.sub.3) which requires the cell to operate at elevated temperature in the order of 1400.degree. F. On the fuel side carbon monoxide is injected into the gas chamber attached to the anode, with carbon dioxide as the product of reaction. Carbon dioxide is mixed with air for injection into the gas chamber attached to the cathode, with a portion of the air being withdrawn from the chamber. While this cell generates electricity in an operation at relatively high temperature with resultant loss in efficiency, an advantage is gained in that high catalytic efficiency is not required.
Fuel cells of other designs are of lesser interest to the present invention, but those skilled in the art will recognize that many other designs could be used in the practice of the present invention.
No particular novelty is claimed in producing useful fuels from coal in situ. No particular novelty is claimed in the use of fuel cells to generate electricity. Novelty is claimed in combining an in situ coal gasification project with a battery of fuel cells in order to convert chemical energy into electricity.